That's if you're under the ideology that wins/losses should be the ranking factor, it's a tautology. I think the rank should be a 1.0 k/d ratio (or something involving assists as well). That way, if you are playing with randoms but against teams, it would be more balanced. I'm speaking about slayer gametypes, btw. If it were objective game types, the objectives should be a higher factor.
Assists should count for half as much as kills then, that would at least help. Also I previously said I think wins should still factor in, they just shouldn't be the end all be all. I'm all over the place though, my bad.
Assist and win did matter in in Rank reach, that didnt stop people for doing that, because Kill were always more important than Assist. what you are proposing already was done and it didnt work.